Halo 2 Walkthrough
That Old, Familiar Feeling
You head forward to the grey area and get a checkpoint. Go across and down the bridge. You find dead flood in various spots. Go on through the white tunnel.

Cut scene - you see a woman looking at a tentacle, and then she grabs it and leans out to get the floating key. She gets the key, and the Sergeant saves her and pulls her back to safety. An invisible guy (i.e. you, the Arbitor) comes along. The Arbitor knocks out the two humans and gets the key. "Excellent wrok, Arbitor" says the grey haired Covenant guy, who takes the key / icon from you. He says he is Tharderus, Chieftain of the Brutes. You ask why he gets the key and he says "They ordered me to do it". He then knocks you into the hole.

Now you see the Master Chief in the tentacles of a giant Seymour like creature (from Little Shop of Horrors - a venus fly trap). Seymour has the Master Chief, the Arbitor, the Regret leader, and Guilty Spark. He says "I am a monument to all your sins". The prophet Regret keeps saying "Nothing can be done until my sermon is complete." Guilty spark says "The oracles know nothing of containment!" The plant says "If you will not hear the truth, then I will show it to you." He likes to speak in rhymes, and tells you both (Master Chief and Arbitor) to go looking for the key before it's too late.